UPDATE: Cameron Bancroft has been charged with attempting to alter the condition of the ball, and Australia captain Steve Smith has admitted the side's senior players hatched a plan that the opener acted out. Click here for the full story

Former South Africa captain Graeme Smith believes Australia batsman Cameron Bancroft has tampered with the ball with a foreign object that could be sandpaper on day two of the third Test in Cape Town.

Bancroft was captured putting a yellow object down the front of his pants moments before the umpires seemingly inquired what was in the fielder’s pockets.

Footage later broadcast showed Bancroft rubbing the ball and then seemingly putting an object back in his pocket, although it’s unclear what the object was.

"In my opinion he has tampered with the ball, and used an object to do that," Smith said on commentary after the tea break.

"Clearly he's hiding something away from the umpires and when they approach him he pulls something outside of his pocket.

"It is damning in my mind.

"You can see that he's taking something out of his pocket, using it on the ball, and once the message comes out (to the umpires) he's clearly hiding it away. When he gets approached he takes out the old sunglasses cleaner."

The former Proteas captain, reviewing the vision at the tea interval alongside Test legend Shane Warne, suggested the item might be sandpaper.

Cameron Bancroft on day three in Cape Town // SuperSport

Having watched cricket for a period time it does look like he's using something to alter the ball," Smith said on SuperSport.

"And it all looks a bit sheepish when he's been told and he tries to hide it in his crotch.

"It does seem like a bit of sandpaper. We saw the incident in PE between AB (de Villiers) and David Warner having an argument about the tape on his hands and various other things.

"The footage doesn't look good."

Warne said if the Australian has done something wrong he should own up.

"I don't care who you are you can't tamper with the ball," Warne said.

"We don't know, we can't make accusations.

Cameron Bancroft on day three in Cape Town // SuperSport

"I don't care if it's Australia or South Africa, you just can't do the things it looks like we all think it's doing.

"To me that would be really disappointing.

"I know the Australian sides I played in never did anything like that.

"I feel a bit for Cameron Bancroft because I don't think he's taken it upon himself to do something and put it in his pocket.

"Who's told him to do that? It's important to find out that. I think we've got to get to the bottom of why that has happened and what was it.

"You've got to own up. You've been caught, you've got to own up and say what was it you were hiding. You can't have that in the game."

Ball tampering is a Level 2 offence in the ICC Code of Conduct, which carries a maximum 100 per cent fine and up to four demerit points, which equates to a one-Test suspension.

Bancroft speaks to umpires on day three // SuperSport

If Bancroft is found to be illegally changing the condition of the ball, Smith says Australia's captain and coach must also face the music.

"If it is proven what the footage we're seeing is correct you've got to ask some tough questions of Steve Smith and Darren Lehmann," Smith said.